PALEOCEANOGRAPHIC VARIATIONS OF THE WESTERN PACIFIC WARM POOL DURING THE MIDDLE PLEISTOCENE CLIMATE TRANSITION

The quantitative census of planktonic foraminifera from the upper 25 m of ODP 130 Site 807A, combined with the paleotemperature data estimated by using faunal transfer function and the oxygen isotopic record, reveal the periodical changes of sea surface temperature (SST) and thermocline in the Western Pacific Warm Pool (WPWP) during the last 1.6 Ma. Our results indicate that winter SST varied over~5℃ in the glacial-interglacial cycles and the depth of thermocline (DOT) has shoaled gradually since 1.6 MaBP. Compared with the South China Sea (SCS) and the Eastern Equatorial Pacific SSTs and DOT changes, the sea surface water of the WPWP more closely connected with the southern SCS, while the northern SCS seemed to be mainly controlled by the Asian winter monsoon. Meanwhile, the DOT of the SCS and Western and Eastern Pacific became shallower on different scales for the past 1.6 Ma. It is found that the Middle Pleistocene Climate Transition (MPT) was probably the critical boundary for many paleoceanographic changes. Taking the MPT as a time boundary, a cross-spectral analysis was made between the winter SST,Δδ¹⁸O _{P.obliquiloculata-G.ruber} and the Earth Orbital Parameter ETP for two time slices of 0~0.9 and 0.9~1.6 Ma respectively. This result shows that the paleoceanographic changes in the WPWP followed the global climate periodicity transition from 41 to 100 ka and displayed a typical tropical forcing character.